High meso-surface area and high acid site density pentasil zeolite for use in xylene conversion

ABSTRACT

A process for the production of para-xylene is presented. The process includes the isomerization of C8 aromatics to para-xylene utilizing a new catalyst. The new catalyst and designated as UZM-54 is represented by the empirical composition in the as synthesized and anhydrous basis expressed by the empirical formula of: 
       M m   n+ R 1 r1   p   1   + R 2 r2   p   2   + Al 1-x E x Si y O z    
     where M is an alkali, alkaline earth, or rare earth metal such as sodium and/or potassium, R 1  and R 2  are organoammonium cation and E is a framework element such as gallium, iron, boron, or indium. UZM-54 are characterized by unique x-ray diffraction patterns, high meso surface area, low Si/Al ratios.

FIELD OF THE INVENTION

The present invention relates to the use of a new family ofaluminosilicate zeolites, having a designation of UZM-54. UZM-54 ischaracterized by unique x-ray diffraction patterns, high meso-surfacearea and low Si/Al ratio compositions.

BACKGROUND

Most new aromatics complexes are designed to maximize the yield ofbenzene and para-xylene. Benzene is a versatile petrochemical buildingblock used in many different products based on its derivation includingethylbenzene, cumene, and cyclohexane. Para-xylene is also an importantbuilding block, which is used almost exclusively for the production ofpolyester fibers, resins, and films formed via terephthalic acid ordimethyl terephthalate intermediates. Accordingly, an aromatics complexmay be configured in many different ways depending on the desiredproducts, available feedstocks, and investment capital available. A widerange of options permits flexibility in varying the product slatebalance of benzene and para-xylene to meet downstream processingrequirements.

A prior art aromatics complex flow scheme has been disclosed by Meyersin the Handbook of Petroleum Refining Processes, 2d. Edition in 1997 byMcGraw-Hill.

U.S. Pat. No. 3,996,305 to Berger discloses a fractionation schemeprimarily directed to trans alkylation of toluene and C₉ alkylaromaticsin order to produce benzene and xylene. The trans alkylation process isalso combined with an aromatics extraction process. The fractionationscheme includes a single column with two streams entering and with threestreams exiting the column for integrated economic benefits.

U.S. Pat. No. 4,341,914 to Berger discloses a transalkylation processwith recycle of C₉ alkylaromatics in order to increase yield of xylenesfrom the process. The transalkylation process is also preferablyintegrated with a paraxylene separation zone and a xylene isomerizationzone operated as a continuous loop receiving mixed xylenes from thetransalkylation zone feedstock and effluent fractionation zones.

U.S. Pat. No. 4,642,406 to Schmidt discloses a high severity process forxylene production that employs a transalkylation zone thatsimultaneously performs as an isomerization zone over a nonmetalcatalyst. High quality benzene is produced along with a mixture ofxylenes, which allows para-xylene to be separated by absorptiveseparation from the mixture with the isomer-depleted stream being passedback to the trans alkylation zone.

U.S. Pat. No. 5,417,844 to Boitiaux et al. discloses a process for theselective dehydrogenation of olefins in steam cracking petrol in thepresence of a nickel catalyst and is characterized in that prior to theuse of the catalyst, a sulfur-containing organic compound isincorporated into the catalyst outside of the reactor prior to use.

The importance of para-xylene production has led to the development ofmany different processes. However, there are losses associated withthese processes. Improvements to reduce and minimize losses areimportant for the economics of para-xylene production.

SUMMARY

A first embodiment of the invention is a process for the production ofpara-xylene, comprising passing a mixture of hydrocarbons comprisingxylenes to an isomerization reactor, operated at isomerization reactionconditions, to form a reaction mixture over an isomerization catalyst,and to generate an effluent stream comprising p-xylene; wherein theisomerization catalyst is UZM-54.

The UZM-54 aluminosilicate zeolite is a microporous crystallinestructure comprising a framework of AlO₂ and SiO₂ tetrahedral units, andan empirical composition in the as synthesized and anhydrous basisexpressed by the empirical formula of M_(m) ^(n+)R_(1 r1) ^(p) ₁⁺R_(2 r2) ^(p) ₂ ⁺AlSi_(y)O_(z) where M is at least one exchangeablecation selected from the group consisting of alkali and alkaline earthmetals, “m” is the mole ratio of M to Al and varies from about 0 toabout 1, R₁ is at least one organoammonium cation selected from thegroup consisting of quaternary ammonium cations, diquaternary ammoniumcations, “r₁” is the mole ratio of R₁ to Al and has a value of about 0.1to about 3.0, R₂ is at least one organoammonium cation selected from thegroup consisting of protonated alkanolamines, protonated amines,protonated diamines, and quaternized alkanolammonium cations, “r₂” isthe mole ratio of R₂ to Al and has a value of about 0 to about 3.0, “n”is the weight average valence of M and has a value of about 1 to about2, “p₁” is the weighted average valence of R₁ and has a value of about 1to about 2, “p₂” is the weighted average valence of R₂ and has a valueof about 1 to about 2, “y” is the mole ratio of Si to Al and varies fromgreater than 11 to about 30 and “z” is the mole ratio of O to Al and hasa value determined by the equation z=(m·n+r₁·p₁+r₂·p₂+3+4·y)/2 and it ischaracterized in that it has the x-ray diffraction pattern having atleast the d spacing and intensities set forth in the following Table:

TABLE 2Θ d(Å) I/Io 7.91-8.05 10.83-11.16 vs 8.84-9.01 9.80-9.99 vs14.87-14.91 5.93-5.95 w-m 15.51-15.65 5.65-5.70 w 15.91-16.12 5.49-5.56w 20.41-20.59 4.31-4.34 w 20.82-20.94 4.25-4.43 w 23.25-23.61 3.76-3.82vs 23.84-23.92 3.71-3.72 m 24.35-24.75 3.59-3.65 m 26.80-26.95 3.30-3.32w 29.33-29.46 3.02-3.04 w 30.01-30.13 2.96-2.97 w 30.32-30.32 2.94-2.94w

An embodiment of the invention is one, any or all of prior embodimentsin this paragraph up through the first embodiment in this paragraphwherein the isomerization reaction conditions include a temperaturebetween 190° C. and 350° C. An embodiment of the invention is one, anyor all of prior embodiments in this paragraph up through the firstembodiment in this paragraph wherein the isomerization reactionconditions include a temperature between 220° C. and 270° C. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the first embodiment in this paragraph whereinthe isomerization reaction conditions include a pressure sufficient tomaintain the reaction mixture in the liquid phase. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the first embodiment in this paragraph wherein the pressure isat least 1025 kPa. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the first embodiment inthis paragraph wherein the mixture of hydrocarbons further includesethylbenzene. An embodiment of the invention is one, any or all of priorembodiments in this paragraph up through the first embodiment in thisparagraph where M in the zeolite is selected from the group consistingof lithium, sodium, potassium, cesium, strontium, calcium, barium andmixtures thereof. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the first embodiment inthis paragraph where M in the zeolite is a mixture of an alkali metaland an alkaline earth metal. An embodiment of the invention is one, anyor all of prior embodiments in this paragraph up through the firstembodiment in this paragraph where R₁ in the zeolite is selected fromthe group consisting of dimethyldipropylammonimum,diethyldipropylammonium, propyltrimethylammonium, hexamethonium, andmixtures thereof. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the first embodiment inthis paragraph where R₂ in the zeolite is selected from the groupconsisting of diethanolamine, N-methylethanolamine,2-dimethylaminoethanol, N-methyldiethanolamine, 2-diethylamino ethanol,2-isopropylamino ethanol, 2-diisopropylamino ethanol, 3-dimethylaminopropanol and 2-aminopropanol and mixtures thereof. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the first embodiment in this paragraph wherein the catalyst,UZM-54, is characterized by a zeolite having a microporous crystallinestructure comprising a framework of AlO₂ and SiO₂ tetrahedral units,further including the element E and having the empirical composition inthe as synthesized and anhydrous basis expressed by the empiricalformula of M_(m) ^(n+)R_(1 r1) ^(p) ₁ ⁺R_(2 r2) ^(p) ₂⁺Al_(1-x)E_(x)Si_(y)O_(z) where “m” is the mole ratio of M to (Al+E) andvaries from about 0 to about 1, “r₁” is the mole ratio of R₁ to (Al+E)and has a value of about 0.1 to about 3.0, “r₂” is the mole ratio of R₂to (Al+E) and has a value of about 0 to about 3.0, E is an elementselected from the group consisting of gallium, iron, boron, indium andmixtures thereof, “x” is the mole fraction of E and has a value from 0to about 1.0, “y” is the mole ratio of Si to (Al+E) and varies fromgreater than 11 to about 30 and “z” is the mole ratio of O to (Al+E) andhas a value determined by the equation z=(m·n+r₁·p₁+r₂·p₂+3+4·y)/2. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the first embodiment in this paragraph furthercomprising passing the effluent stream to a para-xylene separation unitto generate a para-xylene process stream and a second stream comprisingmeta-xylene and ortho-xylene. An embodiment of the invention is one, anyor all of prior embodiments in this paragraph up through the firstembodiment in this paragraph wherein the separation unit is anadsorption separation unit and generates and extract stream comprisingpara-xylene and desorbent and a raffinate stream comprising meta-xyleneand ortho-xylene. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the first embodiment inthis paragraph further comprising passing the extract stream to afractionation unit to generate a bottoms stream comprising para-xyleneand an overhead stream comprising desorbent. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the first embodiment in this paragraph wherein the raffinatestream is passed to the isomerization reactor.

A second embodiment of the invention is a process for the production ofpara-xylene, comprising passing a mixture of hydrocarbons comprisingxylenes to an isomerization reactor, operated at isomerization reactionconditions, to form a reaction mixture over an isomerization catalyst ofthe aluminosilicate zeolite UZM-54, and to generate an effluent streamcomprising para-xylene, wherein the catalyst is a zeolite, UZM-54, ofclaim 1 having a microporous crystalline structure comprising aframework of AlO₂ and SiO₂ tetrahedral units, further including theelement E and having the empirical composition in the as synthesized andanhydrous basis expressed by the empirical formula of M_(m)^(n+)R_(1 r1) ^(p) ₁ ⁺R_(2 r2) ^(p) ₂ ⁺Al_(1-x)E_(x)Si_(y)O_(z) where“m” is the mole ratio of M to (Al+E) and varies from about 0 to about 1,“r₁” is the mole ratio of R₁ to (Al+E) and has a value of about 0.1 toabout 3.0, “r₂” is the mole ratio of R₂ to (Al+E) and has a value ofabout 0 to about 3.0, E is an element selected from the group consistingof gallium, iron, boron, indium and mixtures thereof, “x” is the molefraction of E and has a value from 0 to about 1.0, “y” is the mole ratioof Si to (Al+E) and varies from greater than 11 to about 30 and “z” isthe mole ratio of O to (Al+E) and has a value determined by the equationz=(m·n+r₁·p₁+r₂·p₂+3+4·y)/2 and it is characterized in that it has thex-ray diffraction pattern having at least the d spacing and intensitiesset forth in the following Table:

TABLE 2Θ d(Å) I/Io 7.91-8.05 10.83-11.16 vs 8.84-9.01 9.80-9.99 vs14.87-14.91 5.93-5.95 w-m 15.51-15.65 5.65-5.70 w 15.91-16.12 5.49-5.56w 20.41-20.59 4.31-4.34 w 20.82-20.94 4.25-4.43 w 23.25-23.61 3.76-3.82vs 23.84-23.92 3.71-3.72 m 24.35-24.75 3.59-3.65 m 26.80-26.95 3.30-3.32w 29.33-29.46 3.02-3.04 w 30.01-30.13 2.96-2.97 w 30.32-30.32 2.94-2.94w

An embodiment of the invention is one, any or all of prior embodimentsin this paragraph up through the second embodiment in this paragraphwherein the isomerization reaction conditions include a temperaturebetween 190° C. and 350° C. An embodiment of the invention is one, anyor all of prior embodiments in this paragraph up through the secondembodiment in this paragraph wherein the isomerization reactionconditions include a pressure sufficient to maintain the reactionmixture in the liquid phase. An embodiment of the invention is one, anyor all of prior embodiments in this paragraph up through the secondembodiment in this paragraph wherein the pressure is at least 1025 kPa.An embodiment of the invention is one, any or all of prior embodimentsin this paragraph up through the second embodiment in this paragraphwherein the mixture of hydrocarbons further includes ethylbenzene.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art from the following detaileddescription.

DETAILED DESCRIPTION

Para-xylene production is a valuable commercial process, wherein thereduction of losses can entail a significant economic advantage. Onemethod of improving para-xylene yields is to increase the conversionfrom C₈ compounds to para-xylene and to reduce losses during thatconversion. The operating of a liquid phase xylene isomerization reactorusing a conventional MFI catalyst generates a significant xylene lossper pass. The loss is greater than 1.0%. The invention of a newcatalyst, UZM-54, allows for a significant reduction in the xylene loss.The new catalyst has a new zeolitic MFI morphology, high meso-surfacearea and low Si/Al ratios and can achieve comparable para-xylene contentwith xylene losses of around 0.2% or less.

The present invention is a process for the production of para-xylene.The process includes passing a mixture of hydrocarbons including xylenesto an isomerization reactor, operated at isomerization reactionconditions to generate an effluent stream having para-xylene, orp-xylene. The reaction conditions include forming a reaction mixturecomprising C₇-C₉ hydrocarbons and passing the mixture over anisomerization catalyst. The present invention utilizes a new catalystthat reduces the loss of xylenes during the isomerization process. Theisomerization catalyst is a zeolite having a microporous crystallinestructure comprising a framework of AlO₂ and SiO₂ tetrahedral units, andan empirical composition in the as synthesized and anhydrous basisexpressed by the empirical formula of:

M_(m) ^(n+)R_(1 r1) ^(p) ₁ ⁺R_(2 r2) ^(p) ₂ ⁺AlSi_(y)O_(z).

The catalyst comprises M, which is at least one exchangeable cationselected from the group consisting of alkali and alkaline earth metals,“m” is the mole ratio of M to Al and varies from about 0 to about 1, R₁is at least one organoammonium cation selected from the group consistingof quaternary ammonium cations, diquaternary ammonium cations, “r₁” isthe mole ratio of R₁ to Al and has a value of about 0.1 to about 3.0, R₂is at least one organoammonium cation selected from the group consistingof protonated alkanolamines, protonated amines, protonated diamines, andquaternized alkanolammonium cations, “r₂” is the mole ratio of R₂ to Aland has a value of about 0 to about 3.0, “n” is the weight averagevalence of M and has a value of about 1 to about 2, “p₁” is the weightedaverage valence of R₁ and has a value of about 1 to about 2, “p₂” is theweighted average valence of R₂ and has a value of about 1 to about 2,“y” is the mole ratio of Si to Al and varies from greater than 11 toabout 30 and “z” is the mole ratio of O to Al and has a value determinedby the equation:

z=(m·n+r ₁ ·p ₁ +r ₂ ·p ₂+3+4·y)/2.

The catalyst, UZM-54, can be further characterized by its unique x-raydiffraction pattern as at least the d spacing and intensities set forthin Table A:

TABLE A 2Θ d(Å) I/Io 7.91-8.05 10.83-11.16 vs 8.84-9.01 9.80-9.99 vs14.87-14.91 5.93-5.95 w-m 15.51-15.65 5.65-5.70 w 15.91-16.12 5.49-5.56w 20.41-20.59 4.31-4.34 w 20.82-20.94 4.25-4.43 w 23.25-23.61 3.76-3.82vs 23.84-23.92 3.71-3.72 m 24.35-24.75 3.59-3.65 m 26.80-26.95 3.30-3.32w 29.33-29.46 3.02-3.04 w 30.01-30.13 2.96-2.97 w 30.32-30.32 2.94-2.94w

The M in the zeolite can be a mixture of alkali metals and alkalineearth metals, with a preferred M including one or more metals fromlithium, sodium, potassium, cesium, strontium, calcium and barium. TheR₁ cation can be selected from one or more of quaternary ammoniumcations, quaternary phosphonium cations, and methonium cations. The R₁cation can come from an halide compound or a hydroxide compound.Preferred R₁ cations include one or more from dimethyldipropylammonimum,diethyldipropylammonium, propyltrimethylammonium and hexamethonium. TheR2 cation can come from an halide compound or a hydroxide compound.Preferred R2 cations include one or more from diethanolamine,N-methylethanolamine, 2-dimethylaminoethanol, N-methyldiethanolamine,2-diethylamino ethanol, 2-isopropylamino ethanol, 2-diisopropylaminoethanol, 3-dimethylamino propanol and 2-aminopropanol.

The isomerization reaction conditions include a temperature between 190°C. and 350° C., with a preferred reaction temperature between 220° C.and 270° C. The reaction conditions include a pressure sufficient tomaintain the reaction mixture in the liquid phase. In one embodiment,the pressure in the reactor is at least 1025 kPa, with a preferredreactor pressure in the range of 1750 kPa to 2400 kPa.

The feedstream preferably comprises C₈ aromatics, having para-xylene,meta-xylene and ortho-xylene. The feedstream can also includeethylbenzene, wherein the isomerization reactor converts the meta-xyleneand ortho-xylene to para-xylene, and the ethylbenzene to benzene.

The effluent stream leaving the isomerization reactor includespara-xylene is passed to a para-xylene separation unit to generate apara-xylene process stream, and a second stream comprising meta-xylene,ortho-xylene and ethylbenzene. The para-xylene separation unit cancomprise an adsorption separation unit, wherein the para-xylene processstream is the extract stream and the second stream is the raffinatestream. The extract stream and raffinate streams can include adesorbent. The extract stream is passed to a fractionation unit togenerate a bottoms stream comprising para-xylene and an overhead streamcomprising desorbent. The process can further include passing theraffinate stream to the isomerization reactor. The raffinate stream canalso be passed to a second fractionation column to separate thedesorbent from the raffinate stream before passing the raffinate streamto the isomerization reactor.

In another embodiment, the catalyst is characterized by a zeolite havinga microporous crystalline structure comprising a framework of AlO₂ andSiO₂ tetrahedral units, further including the element E and having theempirical composition in the as synthesized and anhydrous basisexpressed by the empirical formula of:

M_(m) ^(n+)R_(1 r1) ^(p) ₁ ⁺R_(2 r2) ^(p) ₂ ⁺Al_(1-x)E_(x)Si_(y)O_(z)

where “m” is the mole ratio of M to (Al+E) and varies from about 0 toabout 1, “r₁” is the mole ratio of R₁ to (Al+E) and has a value of about0.1 to about 3.0, “r₂” is the mole ratio of R₂ to (Al+E) and has a valueof about 0 to about 3.0, E is an element selected from the groupconsisting of gallium, iron, boron, indium and mixtures thereof, “x” isthe mole fraction of E and has a value from 0 to about 1.0, “y” is themole ratio of Si to (Al+E) and varies from greater than 11 to about 30and “z” is the mole ratio of O to (Al+E) and has a value determined bythe equation:

z=(m·n+r ₁ ·p ₁ +r ₂ ·p ₂+3+4·y)/2.

Higher meso-surface area UZM-54 zeolite, show similar results forisomerization activity with respect to the para-xylene/xyleneequilibrium, but has a much lower production of heavy components, orC₁₁₊ aromatics, in the reactor. The high meso-surface area UZM-54produces about 50% less heavier alkylated material in the effluent.Heavier alkylated material represents losses that are generally notrecoverable in an aromatics complex.

Example 1

An aluminosilicate reaction gel was prepared by first mixing 697.60 g ofliquid sodium aluminate (LSA), 2178.08 g of dimethyldipropylammonimumhydroxide (40% SACHEM), 623.14 g of diethanolamine (Aldrich) and14293.27 g of water while stirring vigorously. After thorough mixing,3207.91 g of Ultrasil VN SP 89% was added. After the addition wascompleted, the resulting reaction mixture was homogenized for ½ hour,transferred to a 5-gallon hastelloy stir autoclave. The mixture wascrystallized at 175° C. with stirring at 245 RPM for 92 hours. The solidproduct was recovered by centrifugation, washed with de-ionized waterand dried at 80° C. The product was identified as UZM-54 by XRD.Representative diffraction lines observed for the product are shown inTable 1. The product composition was determined by elemental analysis toconsist of the following mole ratios: Si/Al=13.45, Na/Al=0.0.589. Aportion of the material was calcined by ramping to 600° C. for 2 hoursfollowed by a 5 hour dwell in air. The BET surface area was 416 m²/g,the micropore area was 229 m²/g and the mesopore area was 187 m²/g andthe micropore volume was 0.118 cc/g and mesopore volume was 0.762 cc/g.Scanning Electron Microscopy (SEM) revealed crystals with a roughlyspherical or rosette-like morphology of 10 to 25 nm. Chemical analysiswas as follows: 3.07% Al, 42.9% Si, 1.54% Na, 0.90% N, N/Al=0.56,Na/Al=0.59 Si/Al₂=26.91.

TABLE 1 2θ d(Å) I/I₀ % 7.91 11.16 vs 8.84 9.99 vs 14.87 5.95 w 15.915.56 w 23.26 3.82 vs 23.84 3.72 m 24.43 3.64 m 26.80 3.32 w 30.02 2.97 w45.46 1.99 w

Example 2

The pentasil zeolite of example 1 was formulated into a catalystcontaining 70% zeolite and 30% silica. In the catalyst preparation, thezeolite was mixed with LUDOX AS-40 and Hi-Sil 250 into a Muller mixer.Additional water was added to the Muller mixer, while mixing, untildough with a proper texture for extrusion was formed. The dough wasextruded to form 1/16″ diameter trilobes, which were dried at 100° C.overnight and then sized to a length to diameter ratio of approximately3. The dry extrudates was calcined in a box oven with a flowing air at600° C. for 4 hours to remove the template. The calcined support wasthen exchanged using a 10 wt-% NH₄NO₃ solution at 75° C. for one hour.This was followed by water wash using 20 cc of water per cc ofextrudates. The NH₄NO₃ exchange and water wash was repeated two moretimes. The extrudates was then dried at 120° C. for 4 hours and thenactivated at 550° C. The sodium level of the final catalyst was 0.003%.This is Catalyst A.

Example 3

An aluminosilicate reaction gel was prepared by first mixing 697.60 g ofliquid sodium aluminate (LSA), 2189.02 g of dimethyldipropylammonimumhydroxide (39.8% SACHEM), 623.14 g of diethanolamine (Aldrich) and14282.33 g of water while stirring vigorously. After thorough mixing,3207.91 g of Ultrasil VN SP 89% was added. After the addition wascompleted, the resulting reaction mixture was homogenized for ½ hour,transferred to a 5-gallon hastelloy stir autoclave. The mixture wascrystallized at 175° C. with stirring at 300 RPM for 89 hours. The solidproduct was recovered by centrifugation, washed with de-ionized waterand dried at 80° C. The product was identified as UZM-54 by XRD.Representative diffraction lines observed for the product are shown inTable 2. The product composition was determined by elemental analysis toconsist of the following mole ratios: Si/Al=13.92, Na/Al=0.59. A portionof the material was calcined by ramping to 600° C. for 2 hours followedby a 5 hour dwell in air. The BET surface area was 483 m²/g, themicropore area was 197 m²/g and the mesopore area was 286 m²/g and themicropore volume was 0.101 cc/g and mesopore volume was 0.796 cc/g.Scanning Electron Microscopy (SEM) revealed crystals with a roughlyspherical or rosette-like morphology of 10 to 25 nm. Chemical analysiswas as follows: 2.98% Al, 43.1% Si, 1.50% Na, 0.93% N, N/Al=0.60,Na/Al=0.59, Si/Al₂=27.85.

TABLE 2 2θ d(Å) I/I₀ % 7.97 11.08 vs 8.86 9.97 s 14.91 5.93 w 16.01 5.53w 20.59 4.31 w 20.82 4.26 w 23.28 3.81 vs 23.86 3.72 s 24.51 3.62 m26.95 3.30 w 29.33 3.04 w 30.13 2.96 w 45.13 2.00 w 45.43 1.99 w

Example 4

The pentasil zeolite of example 3 was formulated into a catalystcontaining 70% zeolite and 30% silica. In the catalyst preparation, thezeolite was mixed with LUDOX AS-40 and Hi-Sil 250 into a Muller mixer.Additional water was added to the Muller mixer, while mixing, untildough with a proper texture for extrusion was formed. The dough wasextruded to form 1/16″ diameter trilobes, which were dried at 100° C.overnight and then sized to a length to diameter ratio of approximately3. The dry extrudates was calcined in a box oven with a flowing air at600° C. for 4 hours to remove the template. The calcined support wasthen exchanged using a 10 wt-% NH₄NO₃ solution at 75° C. for one hour.This was followed by water wash using 20 cc of water per cc ofextrudates. The NH₄NO₃ exchange and water wash was repeated two moretimes. The extrudates was then dried at 120° C. for 4 hours and thenactivated at 550° C. The sodium level of the final catalyst was 0.002%.This is Catalyst B.

Example 5 Commercial MFI-23

Pentasil zeolite, purchased from Zeolyst International (lot: CBV 2314),was formulated into a catalyst containing 70% zeolite and 30% silica. Inthe catalyst preparation, the zeolite was mixed with LUDOX AS-40 andHi-Sil 250 into a Muller mixer. Additional water was added to the Mullermixer, while mixing, until dough with a proper texture for extrusion wasformed. The dough was extruded to form 1/16″ diameter trilobes, whichwere dried at 100° C. overnight and then sized to a length to diameterratio of approximately 3. The dry extrudates was calcined in a box ovenwith a flowing air at 600° C. for 4 hours to remove the template. Thecalcined support was then exchanged using a 10 wt-% NH₄NO₃ solution at75° C. for one hour. This was followed by water wash using 20 cc ofwater per cc of extrudates. The NH₄NO₃ exchange and water wash wasrepeated three more times. The extrudates was then dried at 120° C. for4 hours and then activated at 550° C. The sodium level of the finalcatalyst was 0.002%. This is Catalyst C.

Example 6

Catalysts A-C were evaluated for xylene isomerization and ethyl-benzeneretention using a pilot plant upflow reactor processing anon-equilibrium C₈ aromatic feed having the following approximatecomposition in wt-%:

C₇₋₉ non- 0.5 aromatics ethylbenzene 4.5 para-xylene 0.9 meta-xylene64.6 ortho-xylene 29.5

Example 7

Pilot-plant test conditions and results are as follows. The above feedcontacted the Catalyst at a pressure of 3.5 MPa in the liquid phase at aweight hourly space velocity of 10 under a range of temperatures. Theresulting performance measures are shown below:

Catalyst A Catalyst B Catalyst C WHSV, hr −1 10 10 10 Temperature toreach 23 PX/X, ° C. 249 249 298 Xylene Loss, wt % 0.20 0.13 1.22 A11+selectivity, wt % 0.07 0.04 0.11

Note that the “Xylene Loss” is in wt-% defined as “(1-(para, meta, orthoxylene wt % in product)/(-(para, meta, ortho xylene wt % in feed))*100”,which represents material that has to be circulated to another unit inan aromatics complex. Such circulation is expensive and a low amount ofC₈ ring loss is preferred. A11+ represents material that is heavier, andgenerally not recoverable.

While the invention has been described with what are presentlyconsidered the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but it isintended to cover various modifications and equivalent arrangementsincluded within the scope of the appended claims.

What is claimed is:
 1. A process for the production of para-xylene,comprising: passing a mixture of hydrocarbons comprising xylenes to anisomerization reactor, operated at isomerization reaction conditions, toform a reaction mixture over an isomerization catalyst, and to generatean effluent stream comprising p-xylene; wherein the isomerizationcatalyst is characterized by a zeolite having a microporous crystallinestructure comprising a framework of AlO₂ and SiO₂ tetrahedral units, andan empirical composition in the as synthesized and anhydrous basisexpressed by the empirical formula of:M_(m) ^(n+)R_(1 r1) ^(p) ₁ ⁺R_(2 r2) ^(p) ₂ ⁺AlSi_(y)O_(z) where M is atleast one exchangeable cation selected from the group consisting ofalkali and alkaline earth metals, “m” is the mole ratio of M to Al andvaries from about 0 to about 1, R₁ is at least one organoammonium cationselected from the group consisting of quaternary ammonium cations,diquaternary ammonium cations, “r₁” is the mole ratio of R₁ to Al andhas a value of about 0.1 to about 3.0, R₂ is at least one organoammoniumcation selected from the group consisting of protonated alkanolamines,protonated amines, protonated diamines, and quaternized alkanolammoniumcations, “r₂” is the mole ratio of R₂ to Al and has a value of about 0to about 3.0, “n” is the weight average valence of M and has a value ofabout 1 to about 2, “p₁” is the weighted average valence of R₁ and has avalue of about 1 to about 2, “p₂” is the weighted average valence of R₂and has a value of about 1 to about 2, “y” is the mole ratio of Si to Aland varies from greater than 11 to about 30 and “z” is the mole ratio ofO to Al and has a value determined by the equation:z=(m·n+r ₁ ·p ₁ +r ₂ ·p ₂+3+4·y)/2 and it is characterized in that ithas the x-ray diffraction pattern having at least the d spacing andintensities set forth in the following Table: 2Θ d(Å) I/Io 7.91-8.0510.83-11.16 vs 8.84-9.01 9.80-9.99 vs 14.87-14.91 5.93-5.95 w-m15.51-15.65 5.65-5.70 w 15.91-16.12 5.49-5.56 w 20.41-20.59 4.31-4.34 w20.82-20.94 4.25-4.43 w 23.25-23.61 3.76-3.82 vs 23.84-23.92 3.71-3.72 m24.35-24.75 3.59-3.65 m 26.80-26.95 3.30-3.32 w 29.33-29.46 3.02-3.04 w30.01-30.13 2.96-2.97 w 30.32-30.32 2.94-2.94 w


2. The process of claim 1 wherein the isomerization reaction conditionsinclude a temperature between 190° C. and 350° C.
 3. The process ofclaim 2 wherein the isomerization reaction conditions include atemperature between 220° C. and 270° C.
 4. The process of claim 1wherein the isomerization reaction conditions include a pressuresufficient to maintain the reaction mixture in the liquid phase.
 5. Theprocess of claim 1 wherein the pressure is at least 1025 kPa.
 6. Theprocess of claim 1 wherein the mixture of hydrocarbons further includesethylbenzene.
 7. The process of claim 1 where M in the zeolite isselected from the group consisting of lithium, sodium, potassium,cesium, strontium, calcium, barium and mixtures thereof.
 8. The processof claim 1 where M in the zeolite is a mixture of an alkali metal and analkaline earth metal.
 9. The process of claim 1 where R₁ in the zeoliteis selected from the group consisting of dimethyldipropylammonimum,diethyldipropylammonium, propyltrimethylammonium, hexamethonium, andmixtures thereof.
 10. The process of claim 1 where R₂ in the zeolite isselected from the group consisting of diethanolamine,N-methylethanolamine, 2-dimethylaminoethanol, N-methyldiethanolamine,2-diethylamino ethanol, 2-isopropylamino ethanol, 2-diisopropylaminoethanol, 3-dimethylamino propanol and 2-aminopropanol and mixturesthereof.
 11. The process of claim 1 wherein the catalyst ischaracterized by a zeolite having a microporous crystalline structurecomprising a framework of AlO₂ and SiO₂ tetrahedral units, furtherincluding the element E and having the empirical composition in the assynthesized and anhydrous basis expressed by the empirical formula of:M_(m) ^(n+)R_(1 r1) ^(p) ₁ ⁺R_(2 r2) ^(p) ₂ ⁺Al_(1-x)Si_(y)O_(z) where“m” is the mole ratio of M to (Al+E) and varies from about 0 to about 1,“r₁” is the mole ratio of R₁ to (Al+E) and has a value of about 0.1 toabout 3.0, “r₂” is the mole ratio of R₂ to (Al+E) and has a value ofabout 0 to about 3.0, E is an element selected from the group consistingof gallium, iron, boron, indium and mixtures thereof, “x” is the molefraction of E and has a value from 0 to about 1.0, “y” is the mole ratioof Si to (Al+E) and varies from greater than 11 to about 30 and “z” isthe mole ratio of O to (Al+E) and has a value determined by theequation:z=(m·n+r ₁ ·p ₁ +r ₂ ·p ₂+3+4·y)/2.
 12. The process of claim 1 furthercomprising: passing the effluent stream to a para-xylene separation unitto generate a para-xylene process stream and a second stream comprisingmeta-xylene and ortho-xylene.
 13. The process of claim 12 wherein theseparation unit is an adsorption separation unit and generates andextract stream comprising para-xylene and desorbent and a raffinatestream comprising meta-xylene and ortho-xylene.
 14. The process of claim13 further comprising passing the extract stream to a fractionation unitto generate a bottoms stream comprising para-xylene and an overheadstream comprising desorbent.
 15. The process of claim 13 wherein theraffinate stream is passed to the isomerization reactor.
 16. A processfor the production of para-xylene, comprising: passing a mixture ofhydrocarbons comprising xylenes to an isomerization reactor, operated atisomerization reaction conditions, to form a reaction mixture over anisomerization catalyst, and to generate an effluent stream comprisingpara-xylene; wherein the isomerization catalyst, wherein the catalyst isa zeolite having a microporous crystalline MFI structure comprising aframework of AlO₂ and SiO₂ tetrahedral units, further including theelement E and having the empirical composition in the as synthesized andanhydrous basis expressed by the empirical formula of:M_(m) ^(n+)R_(1 r1) ^(p) ₁ ⁺R_(2 r2) ^(p) ₂ ⁺Al_(1-x)Si_(y)O_(z) where“m” is the mole ratio of M to (Al+E) and varies from about 0 to about 1,“r₁” is the mole ratio of R₁ to (Al+E) and has a value of about 0.1 toabout 3.0, “r₂” is the mole ratio of R₂ to (Al+E) and has a value ofabout 0 to about 3.0, E is an element selected from the group consistingof gallium, iron, boron, indium and mixtures thereof, “x” is the molefraction of E and has a value from 0 to about 1.0, “y” is the mole ratioof Si to (Al+E) and varies from greater than 11 to about 30 and “z” isthe mole ratio of O to (Al+E) and has a value determined by theequation:z=(m·n+r ₁ ·p ₁ +r ₂ ·p ₂+3+4·y)/2 and it is characterized in that ithas the x-ray diffraction pattern having at least the d spacing andintensities set forth in the following Table: 2Θ d(Å) I/Io 7.91-8.0510.83-11.16 vs 8.84-9.01 9.80-9.99 vs 14.87-14.91 5.93-5.95 w-m15.51-15.65 5.65-5.70 w 15.91-16.12 5.49-5.56 w 20.41-20.59 4.31-4.34 w20.82-20.94 4.25-4.43 w 23.25-23.61 3.76-3.82 vs 23.84-23.92 3.71-3.72 m24.35-24.75 3.59-3.65 m 26.80-26.95 3.30-3.32 w 29.33-29.46 3.02-3.04 w30.01-30.13 2.96-2.97 w 30.32-30.32 2.94-2.94 w


17. The process of claim 16 wherein the isomerization reactionconditions include a temperature between 190° C. and 350° C.
 18. Theprocess of claim 16 wherein the isomerization reaction conditionsinclude a pressure sufficient to maintain the reaction mixture in theliquid phase.
 19. The process of claim 16 wherein the pressure is atleast 1025 kPa.
 20. The process of claim 16 wherein the mixture ofhydrocarbons further includes ethylbenzene.